Fraktalio logo{ model }

Develop

f { model } It is inspired by DDD, EventSourcing and Functional programming communities, yet implements these ideas and concepts in idiomatic Kotlin/TypeScript/Rust, which in turn makes our code

  • - less error-prone,
  • - easier to understand,
  • - easier to test,
  • - type-safe and thread-safe
the Fraktalio logo: a ledger with the shape of letter F
the Fraktalio logo: a ledger with the shape of letter F
lib/domain.ts
// Restaurant Commands
export type RestaurantCommand =
  | CreateRestaurantCommand
  | ChangeRestaurantMenuCommand
  | PlaceOrderCommand;
  
export type CreateRestaurantCommand = {
  readonly decider: "Restaurant";
  readonly kind: "CreateRestaurantCommand";
  readonly id: RestaurantId;
  readonly name: RestaurantName;
  readonly menu: RestaurantMenu;
};
export type ChangeRestaurantMenuCommand = {
  readonly decider: "Restaurant";
  readonly kind: "ChangeRestaurantMenuCommand";
  readonly id: RestaurantId;
  readonly menu: RestaurantMenu;
};
...

Data

Two standard classes of algebraic types are:

  • - PRODUCT types (i.e., tuples, pair, struct and data classes)
  • - SUM types (i.e., enums and sealed interfaces/classes).

Whereas SUM types let you model the variations within a particular data type, PRODUCT types help cluster related data into a larger abstraction.

Data model is well typed! Notice how RestaurantId, RestaurantName and RestaurantMenu are not of type String which would provide no value and has no meaning from the type system perspective.

Behaviour

The functions offer the algebra of manipulating the data in a compositional manner, effectively modeling the behavior.

  • - decide - exhaustive, pattern matching command handler / takes command and state as parameters, and returns the list of new events
  • - evolve - exhaustive, pattern matching event handler / takes state and event as parameters, and returns the new state
  • - react - exhaustive, pattern matching event handler / takes event, and returns the list of commands that should be executed next.
the Fraktalio logo: a ledger with the shape of letter F
lib/domain.ts
export const restaurantDecider: Decider<
  RestaurantCommand,
  Restaurant | null,
  RestaurantEvent
> = new Decider<RestaurantCommand, Restaurant | null, RestaurantEvent>(
  (command, currentState) => {
    // Decide new events based on the current state and the command
    // Exhaustive pattern matching on the command
    switch (command.kind) {
      case "CreateRestaurantCommand":
      ...

Libraries (Kotlin | Rust | TypeScript)

f{model} in Kotlin

Lightweight Kotlin library enabling functional and reactive domain modeling patterns

f(&model) in Rust

Lightweight Rust library enabling functional and safe domain modeling patterns

f(model) in TypeScript

Lightweight TypeScript library enabling functional and algebraic domain modeling patterns

Demo Applications

LanguageSource Code
Kotlin (Spring)
Kotlin (Ktor)
TypeScript
Rust (Actix-Web Server)
Rust (PostgreSQL Extension)